Does woody encroachment accelerate carbonate weathering?

Abstract:

Carbonate terrains underlie about 20% of Earth’s surface and supply 20-25% of potable water. Due to their rapid kinetics, carbonate terrains respond fast to external perturbations including climate change and land use change. Thus, it is important to understand how external disturbances affect carbonate weathering. In Konza Prairie Biological Station (KPBS), a tall grass-prairie mero-karst catchment in Kansas, stream solute concentrations and carbonate weathering rates have been increasing in the past 3 decades. Woody encroachment has been suggested as a possible driver for this trend, possibly due to increasing groundwater recharges and / or the associated downward fluxes of carbon dioxide. The effects of these two changes on calcite dissolution were studied using a watershed reactive transport model BioRT-Flux-PIHM (BFP). The subsurface carbon dioxide concentration data and groundwater level data and chemistry (Ca, Mg, HCO3) of soil water, groundwater, stream water and precipitation were used to set up the subsurface conditions and constrain the flow partitioning and carbonate weathering rates. Though both factors can be important, we hypothesize that an increase in soil carbon dioxide can lead to increased calcite weathering more than the increased groundwater flow. Interestingly, woody encroachment can also modify the evapotranspiration pattern of the catchment which in turn can influence carbonate dissolution in the catchment. The impact of land use change on weathering can be significant in carbonate terrains. Due to the fast response of calcite dissolution to external perturbations, it can mitigate climate change at shorter time scales than silicate weathering. Understanding how land use change temporarily disturbs the carbon cycle may help guide the way policies are crafted to counter climate change.